1. Field of the Invention
The present invention relates generally to methods for fabricating read sensors for magnetic heads, and more particularly to methods for fabricating the first magnetic shield of a sensor.
2. Description of the Prior Art
Magnetic heads for hard disk drives typically contain a read head element for reading magnetic data bits from the magnetic media disk, and a write head for writing magnetic data bits onto the magnetic media disk. Focusing on the read head element, a typical prior art read head includes a magnetoresistive sensor element in which the electrical resistance of the sensor is influenced by the magnetic field of a data bit that passes close to the sensor. To avoid interference from neighboring data bits and other local magnetic fields, the sensor is disposed between two magnetic shield layers that serve to screen out such interfering magnetic fields. In order to achieve greater areal data storage density within the magnetic media, magnetic data bits are written in increasingly smaller sizes, and the magnetic shields must therefore be spaced closer together in order to effectively perform their shielding task. As a result of the narrowing of the gap between the magnetic shields, the various layers of materials that form the magnetic sensor structure are likewise made thinner. Where electrical insulation layers are made thinner as a part of this process the likelihood of electrical shorts between sensor components increases. Additionally, it becomes more important that the thinner layers and structures be made as planar as possible in order to avoid topological problems and variations in the thickness and properties of these layers. The present invention focuses upon topological features related to the first magnetic shield layer.
In prior art magnetic head fabrication processes, a patterned bilayer photoresist milling mask is fabricated upon the first magnetic shield, and pockets are milled within the first magnetic shield at openings formed in the mask, such that an unmilled centrally disposed shield surface area remains for the fabrication of the sensor thereabove. A fill layer is next deposited across the wafer, and within the pockets. The mask is removed and a first insulation layer (G1) is deposited. The MR sensor is fabricated above the central shield area, and electrical leads are subsequently fabricated to project from the sensor towards the electrical interconnects of the magnetic head. The milling of the pockets typically creates an unwanted deposit of milled shield material, termed fences, at the upper edges of the pockets due to redeposition of shield material during the ion milling process. Also insulation voids are often created at the upper edges of the pockets due to shadowing effects proximate the fences. In prior art magnetic heads where the spacing between the shields was relatively large, the layers of materials forming the sensor were also relatively thick, and the redeposited shield material fences and voids were not of significant concern. However, in more advanced heads, where the shields are made closer together and the sensor layers are made correspondingly thinner, the redeposited shield material fences and the voids, and other topological anomalies of the prior art magnetic head fabrication process become significant. Electrical shorts and corrosion effects become serious problems. The present invention provides a fabrication method which avoids these problems.